Water clarification using alkalisoluble water-insoluble cellulose derivative coagulation aid



United States Patent "ice Walter E. Gloor, Wilmington, DeL, assignor to Hercules Powder Company, Wilmington, Del., a corporation of Delaware No Drawing. Application November 29, 1951,

Serial No. 259,019

10 Claims. I (Cl. 2 1023) This invention relates to a process for the purification and clarification of water. In a specific aspect this invention relates to a process for removing contaminating materials from water by coagulation. In a morespecific aspect this invention relates to an improvedcoagulation process for the removal of contaminants from water wherein a novel coagulant aid is employed.

This application is a continuation-in-part of the copending application, Serial No. 218,531, filed March 30, 1951, now abandoned.

The removal of contaminating materials from water represents an important problem in the purification and clarification of both potable and industrial waters, and it is also an important problem in the treatment of sewage and industrial wastes. Various methods are used for the eradication of contaminants from water, and in these methods coagulation procedures are rather extensively employed, particularly for the removal of turbidity and color bodies which are present as a suspension of finely-divided particles. Also, coagulation procedures remove a large proportion of the bacteria from contaminated water. C- agulation procedures depend upon the use of compounds, known as coagulants, to remove turbidity, color bodies and bacteria from contaminated water by formation of a floc in the water. As floc settles out of the water or as it is removed by some other means, it removes contaminants from the water, and in this manner the water is purified and clarified.

The desired goal in a coagulation procedure is to obtain the maximum degree of clarification with a minimum expenditure for coagulants and treatment facilities. It is desirable that the floc settle relatively rapidly. It is also desirable that the floc be relatively tough in order that it will not break up or disintegrate into small particles while the water containing it is being conveyed to a filter bed or other separation means. It is also desirable that the addition of the coagulant be effective for the removal of the contaminants with the use of a minimum amount of 4 and improved coagulant aids for the removal of contaminants from water by coagulation.

Further and additional objects of thisinvention will be apparent from the ensuing detailed disclosure.

In accordance with this invention it has been found that the above objects and purposes can be achieved by the addition of a water-insoluble cellulose derivative to a contaminated water that is being purified by a coagulation process. The presence of the cellulose derivative causes the floc to settle more rapidly; the floc produced in the presence of the cellulose derivatives is relatively difiicultly 2,728,724 Patented Dec. 27, 1955 presence of the cellulose derivative as a coagulant aid makes it possible to use considerably smaller quantities of coagulant.

The invention can be fully understood by referring to the following specific examples which demonstrate the advantages of employing water-insoluble cellulose derivatives as coagulant aids. In the various examples p. p. m. represents parts by weight per million parts by weight of water.

Example 1 Five p. p. m. of a commercial grade of ferric sulfate was added to a turbit contaminated water and hydroxyethyl cellulose (HEC) containing 0.35 hydroxyethyl substituent per anhydroglucose unit, when employed, was added to the water as a suspension prepared by dissolving 10 g. of hydroxyethyl cellulose in 40ml. of 3N aqueous solution of sodium hydroxide and diluting the resulting solution to one liter with water. After addition of the ferric sulfate and hydroxyethyl cellulose, when employed, .to the water, the mixture was agitated for a period of 30 to 45 minutes, and then the fioc was allowed to settle. The following data were observed:

Percent Floe Settled in- Appearance p. p. m. HEG of Filtered 5 15 30 1 2 Water min. hr. hr.

Slightly turbid.

Almost clear.

Example 2 A procedure similar to that employed in Example 1 was used, but in this procedure 20 p. p. in. of ferric sulfate Example 3 A procedure similar to that described in Example 1 was employed with the exception that the hydroxyethyl cellulose was added to the water as a dry powder instead of in the form of a suspension. The following data were observed:

Appearance of Filtered I). 11. I11. HEC Water Turbid. Very slightly turbid.

Example 4 Two'runs were made by adding 25 p. p. m. of ferric chloride to a contaminated water with 0 and 4 p. p. m. of hydroxyethyl cellulose (D. S. 0.35), respectively. In the run using only ferric chloride no floc was formed, butin the run using 4 p. p. m. of hydroxyethyl cellulose a floc formed and contaminants were removed from the Water. Three additional runs were made by adding 34 p. p. m. of

'ferric'chloride to water from a similar source with 0, 2 and disintegrated;and to obtain the desired clarification the 4 p. p. m. of hydroxyethyl cellulose, respectively. It was noted that the addition of the hydroxyethyl cellulose lowered the color and turbidity of the water as well as its iron and manganese content, and a decrease in the required "flocculation time was also noted.

Example 5 A procedure similar to that described in Example .1

was employed with the exception that 2.5 p. p. m. of alum was used with varying amounts of'hydroxyethyl Example 9 Alkali-soluble, water-insoluble oxidized cellulose (Hemo-Pack) was added in the form of a diluted sodium hydroxide dispersion to contaminated water to which cellulose (D. S. 0.33). The following data were ob- 5 27.5 p. p. m. of alum was added as a coagulant. The served following data were observed:

Pei-cent Floc Settled in p p m Percent Floc Settled iii-- Appearance of Oxidized p. p. m. HEG l 15 so my Fltered oellullse 5min. 15 min. 30 min. 60 min. 120 min. H1111. 111111. 1111B.

1 2 3 4 7 0 3 5 6 12 65 Almost clear. 15 4O 75 85 93 1 4 s 12 30 70 Do. 15 55 as so 95 2 5 2c 55 75 95 Very slight haze. 40' 60 so 95 10 30 50 75 95 Example 6 Example 10 A procedure similar to that described in Example 1 was employed with the exception that p. p. m. of alum was used with varying amounts of hydroxyethyl cellulose (D. S. 0.33). The following data were ob- Alkali-soluble, water-insoluble methyl ethyl cellulose was added in the form of a diluted sodium hydroxide dispersion to contaminated water to which 10 p. p. m. of ferric sulfate was added as a coagulant. The followserved.

mg data were observed Percent Floc Settled in- D V Appearance 0! v IL Percent Flee Settled inp. p. m. HDC 5 5 0 h Filtered Water Methgl' ethyl min. min. min. 061M058 5min. 30min. 60min. 120 min.

2 4 8 75 Almost clear. 5 25 75 3 8 18 45 86 Do. 10 75 85 2 4 20 90 Do.

In another run the methyl ethyl cellulose was em- Example 7 Alkali-soluble, water-insoluble sodium carboxymethylcellulose (CMC), D. S. 0.19, was added in the form of a water dispersion to contaminated water to which 10 p. p. m. of ferric sulfate was also added as a coagulant. The following data were observed:

Percent Floc Settled inp. p. m. CMC

30 min. min. 120 min.

Sodium carboxymethylcellulose having the same degree of substitution was added in the form of a diluted sodium hydroxide dispersion to contaminated water to which 15 p. p. m. of alum was also added as a coagulant. The following data were observed:

Percent Floc Settled inp. p. m. 0M0

30 min. 60 min. 120 min.

Example 8 Alkali-soluble, water-insoluble sodium sulfoethyl cellulose (SEC), D. S. 0.122, was added in the form of a water dispersion to contaminated water to which 27.5

p; p. m Percent Floc Settled in- Methyl ethyl mums 5 min. 30 min. 60 min. 120 min.

Example 11 Alkali-soluble, water-insoluble methyl cellulose having a viscosity of 15 cps. was added in the form of (1) a diluted sodium hydroxide dispersion and (2) a water dispersion to contaminated water to which alum was added as a coagulant. The following data were observed:

p m. Percent Floo Settled in Methyl 0611mm 5 min. 30 min. 00 min. min.

7 as 50 s0 8 60 so 90 s 55 7c 85 The above examples clearly point out the utility and desirable features of this invention. For example, one of the outstanding features of this invention is shown by a comparison of the data in Examples 5 and 6. The water that was purified in both of these examples was taken from the same source. If we compare the results obtained in the run in Example 6 where 15 p. p. rn. 0f alum and no hydroxyethy'l cellulose was used with the results obtained in the run in Example 5 where 2.5 p. p. In. of alum and 2 p. p. m. of hydroxyethyl cellulose were used, it is apparent that the fioc settled more rapidly in the latter case while employing considerably less alum. Thus, by using only 2 p. p. m. of hydroxyethyl cellulose a considerable decrease in the time required for settling of the floc and in the amount of coagulant required is obtained.

It is realized that each water supply is unique, hence the resultsv shown above, obtained using various waters from. different localities, may not be entirely concordant with respect to the settling rates of the coagulant taken by itself nor with respect to the magnitude of the benefit contributed'by thewater-insoluble cellulose derivative. However, in all cases a definite advantage was shown by the presence of the cellulose derivative.

The cellulose derivatives of this invention are waterinsoluble and alkali-soluble, and typical examples of these derivatives that can be used are hydroxyalkyl celluloses, such as hydroxyethyl cellulose and the like, the free acid form of carboxyalkyl celluloses, such as carboxymethylcellulose and the like, salts of carboxyalkyl celluloses, such as the alkali metal, ammonium, amine, magnesium salts of carboxymethylcellulose, and the like, the free acid form of sulfoalkyl celluloses, such as sulfoethyl cellulose and the like, salts of sulfoalkyl celluloses, such as the alkali metal, ammonium, amine, magnesium salts of sulfoethyl cellulose, and the like, mixed alkyl celluloses, such as methyl ethyl cellulose and the like, alkyl celluloses, such as methyl cellulose and the like, oxidized cellulose, cellophane, and the like. The term water-insoluble is intended to mean that the cellulose derivatives do not form colloidal solutions in water. The terms waterinsoluble and alkali-soluble are well known and commonly used in the art of cellulosic derivatives, and the water solubility and alkali solubility of a cellulose derivative are readily determinable by admixing the derivative with water or an alkali solvent, such as the case may be, and then noting whether the derivative enters into solution with the solvent. In most instances the solubility characteristics of a cellulose derivative are determined by the degree of substitution or number of substituents per anhydroglucose unit. However, the solubility characteristics of a cellulose derivative of a given degree of substitution are subject to variation and dependent upon such factors as the uniformity of substitution, the method of preparation, and the like. It will be understood that the cellulose derivatives of this invention possess the necessary degree of substitution and/or are prepared in the necessary manner to impart alkali solubility and water insolubility to the derivative. Sodium carboxymethylcellulose having a degree of substitution below 0.35 is regarded as water-insoluble, and at a degree of substitution of 0.35 this derivative becomes partially water-soluble. Its water solubility increases as the degree of substitution increases, and at a degree of substitution of about 0.4 to 0.5 this derivative becomes completely water-soluble. Similarly, sodium sulfoethyl cellulose having a degree of substitution below about 0.28 td'0.3 is regarded as water-insoluble, and at higher degrees of substitution this derivative can be regarded as water-soluble. The above specific examples set forth degrees of substitution at which various cellulose derivatives are alkali-soluble and water-insoluble. The cellulose derivatives in those specific examples can be prepared by any of the known procedures for their preparation. a

The hydroxyethyl cellulose that is employed as a coagulant aid in accordance with this invention is alkali-soluble and water-insoluble. It is available commercially, and it can be produced by various methods. One of these methods of producing hydroxyethyl cellulose involves the etherification of an alkali cellulose with ethylene chlorohydrin in the presence of caustic alkali. A detailed method of producing hydroxyethyl cellulose in this manner is described by Dreyfus in his patent, U. S. 1,502,379. Another method of producing hydroxyethyl cellulose in- Volves the interaction of ethylene oxide and cellulose in the presence of aqueous caustic alkali. Either of these methods or any other method known in the art can be employed to produce the hydroxyethyl cellulose that is used to practice this invention. The hydroxyethyl cellulose that is used contains from 0.1 to 0.8, preferably from 0.25 to 0.5, hydroxyethyl. substituent per anhydroglucose unit. These values can also be referred to as the degree of substitution. The hydroxyethyl cellulose that was empl'o'yedin the above specific examples contained either 0.33 or 0.35 hydroxyethyl substituent per anhydroglucose unit. However, it will be recognized that hydroxyethyl cellulose having a greater or lesser degree of substitution can be used in practicing this invention.

As already described, the cellulose derivatives are employed as coagulant aids and in accordance with the above discussion the cellulose derivatives improve upon and hasten the coagulation. Various known coagulants can be employed in carrying out the process. Alum or commercial aluminum sulfate is quite generally used as a coagulant, and it represents the preferred coagulant for this process. It is available commercially, and it is ordinarily represented by the formula Al2(SO4)3.l8HzO. In addition to alum, any of the other known coagulants may be employed. Among these other coagulants are ferric sulfate, ferric chloride, sodium aluminate, lime-soda water softeners, and the like. Any of these known coagulants are quite effective for purifying and clarifying contaminated water, and the cellulose derivatives of this invention can be used to improve upon such coagulation. Also, in coagulation processes it is sometimes necessary to adjust the pH of the water to a desirable pH for flocculation when a particular coagulant is employed. Such pH adjustment is made by addition of either acidic compounds, such as a strong mineral acid, or basic compounds, such as sodium carbonate, lime or caustic, to the water, and the use of such compounds in the coagulation process is within the scope of this invention. The amount of cellulose derivative that is employed in carrying out this invention is quite variable. The above specific examples demonstrate that a concentration of either 0.5 or 1 part per million parts of water is efiective, but, if desired, lower concentration can be used. The maximum concentration employed in the specific examples was 10 parts per million parts of water, and as the examples show, this concentration was also efiective. It will be understood that greater concentrations can be used if desired. However, greater concentrations are not necessary, and for purposes of economy they are not preferred. A concentration within the range of 0.1 to 10, preferably 0.5 to 5, parts by weight per million parts by weight 1 of water is generally suitable for effecting this invention. It will of course be understood that concentrations outside this range can be used without departing from the spirit and scope of the invention.

7 The cellulose derivative can be added to the contaminated water by various methods. For example, it can be added in the form of a dry powder, and Example 3 above demonstrates such a procedure. On the other hand, the cellulose derivative can be added in the form of a suspen- S1011 prepared by dissolving the derivatives in a caustic alkali solution and then diluting the resulting solution with water. This latter method represents the preferred method of introduction to the contaminated water since it is more convenient to handle the cellulose derivative in the suspension form than in the dry powder form, and it is also easier to add the desired amount of cellulose derivative to the water when it is in the form of a suspension rather than in the form of a dry powder. Alternatively, the cellulose derivative can be added, as a solution in dilute caustic soda or as a dispersion in water, to the water being clarified by coagulation. It is also within the scope of this invention to add the cellulose derivative to the contaminated water at various times during the coagulation process. For example, the cellulose derivative can be added to the water prior to the introduction of the coagulant, and improved turbidity removal is effected by introduction of the cellulose derivative in this manner. Similarly, if desired, it can be added to the water after the introduction of coagulant, and alternatively, the cellulose derivative can be added to the water at the same time the coagulant is added thereto. It is preferred to add the cellulose derivative to the contaminated water after the coagulant floc has been formed to obtain improved floc settling and water color.

In order to insure the desired clarification of the contaminated water it is necessary to obtain adequate contacting of the water, the coagulant and the coagulant aid, and such contacting is usually obtained by agitation of the mixture. Length of the period of agitation is dependent upon several variables, such as the design of the equipment, the clarification desired, the coagulant and coagulant aid employed, the amount of coagulant and coagulant aid used, and the like. In the specific examples the period varied from 30 to 45 minutes. The preferred period varies from 30 to 60 minutes, but in some instances the desired clarification is obtained in a period of about 10 minutes. Obviously, longer and shorter periods can be used within the scope of this invention.

The cellulose derivatives of this invention are effective coagulant aids for purifying or clarifying contaminated water in the vertical hydrotreater type of equipment such as the Spaulding Precipitator. This type of equipment makes maximum use of the cellulose derivatives by retaining the derivatives in the treating Zone for a suitable period of time. Also, these hydrotreaters are rather critical in their operation, and the cellulose derivatives tend to stabilize the operation.

The cellulose derivatives of this invention can be used as coagulant aids either singly or in combination with any of the other cellulose derivatives described above as coagulant aids. Also, the cellulose derivatives can be used in some instances in combination with other noncellulosic coagulant aids, for example, polyvinyl acetate.

Various advantages accrue from the use of cellulose derivatives as coagulant aids in the clarification of Water. One of the foremost advantages is the production of a floc which settles faster when a cellulose derivative is employed with the coagulant as compared with those methods where no cellulose derivative is used. This advantage is particularly important since it makes it possible either to increase the amount of contaminated water undergoing treatment or to treat a given quantity of water in a shorter period of time when a cellulose derivative is used, and thus the economy of the clarification operation is greatly improved. Also, the use of the cellulose derivative results in the production of a tougher, relatively difiicultly disintegrated floc. This advantage is of importance when the water containing the fioc is conveyed to a filter bed or other separation means. The floc tends to remain in an integrated form and as such it is readily separable from the water. Also by use of a cellulose derivative it is possible to employ a lesser amount of coagulant to effect a desired clarification of the water. This advantage is also economically desirable. It is also obvious that by reducing the amount of coagulant, the content of dissolved solids and the conductivity of the treated water is reduced, making the water of better quality for numerous commercial uses. With some waters, use of the cellulose derivatives with the usual coagulants improves the taste of the water, reducing or eliminating its astringent quality. Further and additional advantages of this process and alternative methods of operation within the scope of the invention will be obvious from the discussion above.

What I claim and desire to protect by Letters Patent is:

1. In a process for decreasing the turbidity of water wherein a coagulating agent selected from the group consisting of aluminum sulfate and ferric sulfate is employed to form a floc which removes suspended matter causing said turbidity from the water being treated, the improvement which comprises suspending in said Water an alkalisoluble, water-insoluble substituted cellulose ether and contacting said water and coagulating agent with said cellulose ether to hasten the settling of said floc in the process, said cellulose ether being employed in an amount within the range of 0.1 to 10 parts by weight per million parts of water, and settling floc formed in said process from Water thus treated.

2. In a process for decreasing the turbidity of water wherein a coagulating agent selected from the group consisting of aluminum sulfate and ferric sulfate is employed to form a floc which removes suspended matter causing said turbidity from the water being treated, the improvement which comprises suspending in said Water an alkalisoluble, water-insoluble salt of a carboxyalkyl cellulose ether and contacting said water and coagulating agent with said cellulose ether to hasten the settling of said floc in the process, said cellulose ether being employed in an amount within the range of 0.1 to 10 parts by weight per million parts of water, and settling floc formed in said process from water thus treated.

3. The process according to claim 2 wherein the salt of a carboxyalkyl cellulose ether is the sodium salt of carboxymethylcellulose.

4. In a process for decreasing the turbidity of water wherein a coagulating agent selected from the group consisting of aluminum sulfate and ferric sulfate is employed to form a floc which removes suspended matter causing turbidity from the Water being treated, the improvement which comprises suspending in said water an alkali-soluble, water-insoluble salt of a sulfoalkyl cellulose ether and contacting said water and coagulating agent with said cellulose ether to hasten the settling of said floc in the process, said cellulose ether being employed in an amount within the range of 0.1 to 10 parts by weight per million parts of Water, and settling floc formed in said process from water thus treated.

5. The process according to claim 4 wherein the salt of a sulfoalkyl cellulose is the sodium salt of sulfoethyl cellulose.

6. In a process for decreasing the turbidity of water wherein a coagulating agent selected from the group consisting of aluminum sulfate and ferric sulfate is employed to form a fioc which removes suspended matter causing said turbidity from the water being treated, the improvement which comprises suspending in said water an alkali-soluble, Water-insoluble alkyl cellulose ether and contacting said water and coagulating agent with said cellulose ether to hasten the settling of said fioc in the process, said cellulose ether being employed in an amount Within the range of 0.1 to 10 parts by weight per million parts of water, and settling floc formed in said process from water thus treated.

7. The process according to claim 6 wherein the alkyl cellulose is methyl cellulose.

8. In a process for decreasing the turbidity of Water wherein a coagulating agent selected from the group consisting of aluminum sulfate and ferric sulfate is employed to form a floc which removes suspended matter causing said turbidity from the water being treated, the improvement which comprises suspending in said Water an alkalisoluble, water-insoluble hydroxyalkyl cellulose ether and contacting said water and coagulating agent with said cellulose ether to hasten the settling of said floc in the process, said cellulose ether being employed in an amount within the range of 0.1 to 10 parts by weight per million parts. of water, and settling floc formed in said process from water thus treated.

9. The process according to claim 8 wherein the hydroxyalkyl cellulose is hydroxyethyl cellulose.

10. In a process for decreasing the turbidity of water wherein aluminum sulfate is employed as a coagulating agent to form a floc which removes suspended matter causing said turbidity from the water being treated, the improvement which comprises suspending in said water an alkali-soluble, water-insoluble hydroxyethyl cellulose containing from 0.1 to 0.8 hydroxyethyl substituent per anhydroglucose unit and contacting said water and aluminum sulfate with said hydroxyethyl cellulose to hasten the settling of said fioc in the process, said hydroxyethyl cellulose being employed in an amount within the range of 0.1 to 10 parts by weight per million parts of water, and settling floc formed in said process from Water thus treated.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Lange: Handbook of Chemistry, 7th ed., 1949, pp. 780- Wall Apr. 20, 1920 81, Handbook Publ. Inc., Sandusky, Ohio.

Blumenberg Oct. 7, 1930 5 Gloor et a1.: Ind. & Eng. Chem, vol. 42, No. 10, pp. Richter Mar. 10, 19 2150-3, Oct. 1950.

Larson Oct. 8, 1940 Flocdulation as an Aid in the Clarification of Coal Maxwell et al. Apr. 1, 1941 Washery Water, Bureau of Mines, R. I. 3494, pp. 9-11, Fuetterer June 23, 1944 Feb, 1940,

Cahn Sept. 12, 1944 N Am. Dyestuff Reporter, vol. 35, pp. 3045, 1946. Grassie Dec. 25, 1951 

1. IN A PROCESS FOR DECREASING THE TURBIDITY OF WATER WHEREIN A COAGULATING AGENT SELECTED FROM THE GROUP CONSISTING OF ALUMINUM SULFATE AND FERRIC SULFATE IS EMPLOYED TO FORM A FLOC WHICH REMOVES SUSPENDED MATTER CAUSING SAID TURBIDITY FROM THE WATER BEING TREATED, THE IMPROVEMENT WHICH COMPRISES SUSPENDING IN SAID WATER AND ALKALISOLUBLE, WATER-INSOLUBLE SUBSTITUTED CELLULOSE ETHER AND CONTACTING SAID WATER AND COAGULATING AGENT WITH SAID CELLULOSE ETHER TO HASTEN THE SETTLING OF SAID FLOC IN THE PROCESS, SAID CELLULOSE ETHER BEING EMPLOYED IN AN AMOUNT WITHIN THE RANGE OF 0.1 TO 10 PARTS BY WEIGHT PER MILLION PARTS OF WATER, AND SETTLING FLOC FORMED IN SAID PROCESS FROM WATER THUS TREATED. 